1. Field of the Invention
The present invention relates to a semiconductor phosphor nanoparticle, and in particular, to a group 13-group 15 semiconductor phosphor nanoparticle having an improved luminous intensity and luminous efficiency.
2. Description of the Background Art
It is known that a semiconductor crystalline particle (hereinafter, referred to as “crystalline particle”) having a particle size reduced to about exciton Bohr radius exhibits quantum size effect. Quantum size effect refers to a phenomenon that electrons in a substance are no longer able to move freely as the size of the substance decreases, and in such a condition, the energy of the electron is able to assume only specific, rather than arbitrary values.
C. B. Murray et al. (Journal of the American Chemical Society), 1993, 115, pp. 8706-8715 describes a phosphor using a crystalline particle of a group 12-group 16 compound semiconductor as a technique utilizing the quantum size effect. This crystalline particle has a size of generally exciton Bohr radius, and has a characteristic that a wavelength of light generated becomes short as the dimension decreases.
However, such a phosphor using a crystalline particle of a group 12-group 16 compound semiconductor is problematic in reliability and durability, and has a problem that environmental pollutants such as cadmium and selenium are used. Therefore, an alternative material to the group 12-group 16 compound semiconductor has been demanded.
As a material alternative to the group 12-group 16 compound semiconductor, an attempt is made to synthesize a microcrystal of a nitride-based semiconductor. For example, Japanese Patent Laying-Open No. 2004-307679 discloses a phosphor nanoparticle material of a group 13 nitride semiconductor having a core-shell structure wherein an energy condition of a semiconductor nanoparticle surface is stabilized and thus a luminous efficiency is improved by coating the semiconductor nanoparticle with a compound having a larger band gap energy than the semiconductor nanoparticle. Japanese Patent Laying-Open No. 2004-307679 proposes a technique of improving dispersibility by protecting a surface of the core-shell structure with an organic compound.
However, since there are a dangling-bond (unbound hand) and a surface defect in the outermost face of a semiconductor crystalline particle, a phosphor exhibiting an excellent luminous efficiency cannot be obtained only by protecting a core with a shell layer in a core-shell structure of a semiconductor crystalline particle. This also applies to a case where the shell layer has a laminate structure, or a case where a surface of the shell layer is protected with an organic compound.